When mechanisms are fabricated by patterning a single uniform material layer, such as in micromachining of micro devices, an out-of-plane mechanical displacement is often induced by using out-of-plane forces. This often requires hybrid complex assemblies, such as are described in the article by D. Elata, et al, “A Novel Tilting Micromirror with a Triangular Waveform Resonance Response and an Adjustable Resonance Frequency for Raster Scanning Applications,” presented at the TRANSDUCERS 2007 conference, or by irreversibly deforming structural elements in the out-of-plane direction, such as is described for plastic deformation in L. Lin, et al “Microfabricated torsional actuator using self-aligned plastic deformation,” presented at TRANSDUCERS 2003 conference. Fabrication of a slanted beam in a single crystal silicon has been previously demonstrated, as described in the article “Micromachining of {111} plates in [001] oriented silicon,” by J. W. Berenschot, et al, published in Journal of Micromechanics and Microengineering, vol. 8, pp. 104-107, 1998. This can be achieved, for example, by anisotropic wet etching with KOH of single crystal silicon. In a single crystalline silicon wafer with a {100} orientation, anisotropic etching produces {111} surfaces which are slanted relative to the wafer surface. This process may be used to produce flexures with slanted cross-sections, such as are used in the devices described in U.S. Pat. No. 6,781,280 to Y. Ando et al, for “Slider displacement direction conversion mechanism in electrostatic actuator”. One way of achieving beams with slanted cross sections is by using focused ion beam (FIB) milling as described in the paper by Y. Ando, et al, on “Design, fabrication and testing of new comb actuators realizing three-dimensional continuous motions,” published in Sensors and Actuators A-Physical, vol. 97-8, pp. 579-586, 2002. However, by this method one beam is produced at a time and the process is not compatible with parallel mass fabrication of large numbers of devices on a single wafer. Another way of achieving beams with slanted cross sections is by using deep reactive ion etching (DRIE) to micromachine strips of wafers that are mounted on slanted fixtures. Such a process is described by Y. Ando, et al, in “Development of three-dimensional microstages using inclined deep-reactive ion etching,” published in Journal of Micro-electromechanical Systems, vol. 16, pp. 613-621, 2007, where there is shown a dry etch DRIE machine modified such that strips of a wafer substrate can be placed diagonally to the etch direction. Similar functionality can be realized by using flexures with slanted cross-section.
Reference is now made to FIG. 1, which illustrates a prior art cantilever with slanted cross-section. The coordinate system is chosen such that the x-axis is a horizontal (in-plane) direction and the y-axis is a vertical (out-of-plane) direction. When a horizontal force is applied to the edge of the beam, the edge is displaced in both horizontal and vertical directions as shown in FIG. 2. This is because the orientation of the largest principal moment of inertia of the cross-section is tilted relative to the horizontal direction (as shown by the dotted line in FIG. 1b), thereby defining the tilt of the displacement, as is well known in the art of flexing beams. The displacement is proportional to the applied force.
A problem with all of the above described methods and devices is that when MEMS assemblies are manufactured, the simplest and lowest cost production technique is by means of a 2-D plan form, in which the desired 2-dimensional form of the device and its depth features are impressed into the depth of the substrate by means of simple etching processes, as are known in the art. The above described slanted beam structure is not easily compatible with these technologies. Methods are available for such angled etching, as mentioned hereinabove, but they require costly and time consuming additional processing steps.
There therefore exists a need for conventionally fabricated motion conversion devices for use in MEMS assemblies, which overcome at least some of the disadvantages of prior art motion conversion devices.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.